1. Field of the Invention
The present invention relates to a superconductive Pb-Bi-(Te or Sb) system ternary alloy continuous filament with a high superconducting transition temperature (hereinafter referred to as T.sub.c).
2. Related Art Statement
Heretofore, many attempts have been made to develop superconductors with high T.sub.c, which are useful in large-scale engineering applications such as superconducting magnets, power transmission lines, etc. For such applications, superconductors are generally used in the form of ultra-fine continuous filament composing a multi-core wire. Superconductors with high T.sub.c, however, are usually brittle and difficult to fabricate into fine tapes or filaments, so that great many efforts have so far been concentrated on the manufacture of such filaments, etc.
Thereupon, it was found by the applicant, as reported by the article titled "The Glass-Coated Melt Spinning of Superconductors" printed in Trans. J.I.M., 22: 753 (1981), that a superconductive continuous filament could be produced by the glass-coated melt spinning process, i.e. the so-called "Taylor process", whereby fine filament of metal and alloys can be produced directly from the molten state in one stage. Using the Taylor process, the applicant tried the melt spinning of various germanium alloys such as Ge-Pb, Ge-Sn and Ge-Bi system alloys for producing a superconductive continuous filament, and observed the maximum T.sub.c of no more than 7.1.degree. K. for Ge.sub.25 Pb.sub.75 filament and 4.9.degree. K. for Ge.sub.75 Sn.sub.25 filament (Advances in Cryogenic Engineering, Vol. 30: 699-706, Edited by A. F. Clark and R. P. Reed). Further, with respect to Pb-Bi alloy filament, the applicant prepared Pb.sub.80 Bi.sub.20 filament with high T.sub.c of 11.0.degree. K. by using the Taylor process (Trans. J.I.M. Vol. 25: No. 5, 1984) and, furthermore, the applicant and N. Waku confirmed and reported some Pb-Bi-Ge system ternary alloy filaments exhibited superconductivity at a temperature higher than 10.degree. K., especially Pb.sub.49 Bi.sub.33 Ge.sub.18 filament had the maximum T.sub.c of 14.3.degree. K. (J. Mater. Sci., Vol. 20: p. 532, 1985).
Thus, in the above-mentioned experiments, it was found that the addition of germanium and tellurium to tin or lead resulted in the enhancement of T.sub.c. However, further studies have revealed that these filaments are generally very difficult to spin for lack of fiber-formability or spinability of alloys, wherefore the yield and productivity will be extremely low and, moreover, that the high T.sub.c for Pb.sub.80 Bi.sub.20 filament is difficult to reproduce, so that it seems quite probable to have been accidentally obtained within a very narrow composition range.
Accordingly, this applicant launched out further into a series of studies on Pb-Bi-Te and Pb-Bi-Sb system alloys, aiming at obtaining superconductive continuous filaments with high T.sub.c as well as high stability and productivity, which have so far never been investigated, and eventually accomplished the present invention.